Structures such as buildings and bridges, as well as large machinery temporarily fixed to the ground, often vibrate due to either the wind or ground vibrations caused by seismic activity, passing vehicles and trains; vibration of a structure can lead to destruction of that structure. Structures which have been isolated or decoupled from the ground by positioning resilient energy absorbing pads between the structure's support members and the ground are unlikely to be destroyed from damaging winds or ground vibrations. There exists prior art which addresses the issue of protecting or isolating super-structures from wind or ground vibrations. These devices are designed to absorb a substantial amount of the vibrational energy, produced by the wind or ground motion, which has been transmitted to a superstructure. Actual, nonlaboratory use of prior art "seismic isolation" devices indicate they will successfully protect superstructures from wind or ground vibration damage by reducing the total force transmitted to a superstructure and minimizing the response (i.e., the magnitude and frequency of oscillation) of upper level stories. However, due to the horizontal stiffness and dampening characteristics of these prior art devices, they are limited to use under large, heavy superstructures.
Three mechanisms employed by known seismic isolation devices to absorb energy are: (1) friction dampening of a stack of abutting metal or metal alloy plates as disclosed in U.S. Pat. No. 4,633,628 issued to Naser Mostaghel; (2) shear energy absorption through the cyclic deformation, crystallization, recovery and grain growth of lead, combined with utilizing the dampening characteristics of stacked thin layers of cured rubber separated by layers of a stiffener material as disclosed in U.S. Pat. No. 4,593,502 issued to Ian G. Buckle; and (3) minimal shear and viscous dampening by way of a simple, thick, solid cured rubber support. When used as the vibrational energy absorbing means of a seismic isolation device, lead absorbs energy while undergoing a phase change caused by cyclical deformation of the lead, whereas cured rubber absorbs energy through shear and viscous dampening without changing phase.
Seismic activity typically produces ground vibration which has a large horizontal component and a small vertical component; therefore, a seismic isolation device must be designed with both horizontal stiffness and dampening characteristics and vertical stiffness and dampening charactristics that enable the device to absorb large horizontal cyclical deflections and small vertical cyclical deflections as well as support the static load of a structure or machine. Although the Buckle device as disclosed protects superstructures by sufficiently dampening the horizontal and vertical components of vibrations resulting from seismic activity, its horizontal stiffness is such that small structures, for example single family dwellings or small bridges, or large machinery temporarily fixed to either the ground or some member which may vibrate, cannot be adequately protected. Other known devices used to protect structures from seismic activity, such as a solid homogenous cured rubber support, has been shown to be ineffective in protecting the structures from destruction when placed under a structure to absorb ground vibrations; this is due to the viscoelastic, resilient and minimal dampening properties of such known solid cured rubber supports as designed.
It is a primary object of this invention to provide an energy absorbing isolation pad with an elastomeric resilient energy absorbing mechanism which gives greater elasticity in the horizontal direction yet maximizes the absorption of the vibrational energy so as to protect small structures or large machinery (as well as superstructures) from destruction.
It is another object to produce such an energy absorbing isolation pad by proper design of an elastomeric resilient energy absorbing mechanism and a reinforced resilient restraining shell, to adequately support a static load such as that produced by a small structure or large machinery (as well as superstructures), yet allow said isolation pad to cyclically deform and/or vibrate in the vertical and transverse/horizontal directions when forces are applied to the isolation pad.
It is yet another object to produce such an energy absorbing isolation pad by proper design of an elastomeric resilient energy absorbing mechanism to allow for ease of said isolation pad customization for loads with different structural characteristics.
It is a further object to produce such an energy absorbing isolation pad by proper simplified design to minimize cost of production.